Naturally Increase the Fertility of Your Garden

Thursday, August 28, 2008

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Maybe this whole gardening thing is new to you. If you are just starting out, you don’t have a great pile of compost yet, or the money to invest in it. Perhaps your soil is old and tired, or used to be a lawn or even a parking lot. Whatever your gardening situation, if you need to increase the fertility and texture of your garden with minimal effort, here’s a method to consider. It’s called cover cropping. It was in use long before chemical fertilizers hit the market (you do know that those synthetic fertilizers were available after WWII only because the munitions factories were shutting down and there was an excess of nitrogen on hand, right?). Cover crops actually can accomplish several useful chores depending on what plants you choose to grow.

The idea is simple: sow your farm or garden with one or more plants that can open up the soil with their roots, perhaps fix atmospheric nitrogen, or even deposit pathogen-fighting compounds into the soil. Before the cover crop gets too woody or blooms to set seeds (some of these plants will sound like weeds and they can be if allowed to self-sow), it is mowed down and tilled into the soil. To accomplish this, you will need some elbow grease, but little finesse. A couple of passes with a string trimmer or a machete may be needed first to whack the tallest species down to size. Then, your regular lawnmower should work, set at its highest setting, to reduce the leaves and stems to plant confetti. If you don’t own a rototiller to turn the material into the soil efficiently, they are available for just a few dollars at rental agencies. Once everything is incorporated, the plant material decomposes, adding organic material to the soil and contributing whatever other qualities it might be capable of. Here’s a rundown of plants to use as a cover crop and the benefits they can confer. Seed for individual species is available, but you may find that seed sellers offer some mixes of several species. The choice is yours.

Legumes are traditional cover crops because their claim to fame is that they pull nitrogen out of the air and sequester it in their roots. Tilling the plants into the soil after their season adds significantly to the overall fertility of the soil. There are several to choose from. Vetch (Vicia species) is an old standby. It is quite often included in cover crop seed mixes. Somewhat of a rambler, it will definitely need to be mowed down so that its vining stems don’t just wrap around the tines of your tiller. Fava beans (V. faba) are delicious, edible beans, but for this purpose, the plants should be cut down just as they begin to bloom for the best soil building. To achieve maximum benefit from their ability to fix nitrogen, it helps to inoculate the soil with the beneficial bacteria as you are sowing the seed. They greatly aid the process by forming symbiotic relationships with the roots of the plants. Another bean relative, clover, is also great at fixing nitrogen and never gets very woody, making it easier to shred and till in. Also in this family is alfalfa, which can be grown as a forage plant for livestock, but also serves well as a cover crop.

If nitrogen is not your goal, there are some grass species that also appear in many of the cover crop seed mixes. Rye and barley are typical. They have fibrous root systems that are excellent for breaking up the soil and then, when the whole plant is tilled in, roots, stems, and leaves greatly contribute to the organic content of the soil.

Unlike rye and barley, which are true grasses and related to actual wheat, buckwheat (Fagopyrum) is in another family altogether. The nutritious seeds of buckwheat have been grown for centuries and its value as a cover crop continues another long tradition. Another great candidate for cover cropping is mustard (there are several species of worth). Not only will it add the requisite organic material, but recent studies show that it releases glycosinolates into the soil. These chemicals are having some success at inhibiting the growth of harmful root nematodes and even some pathogenic fungi.

Fall is an excellent time to plant a cover crop. The seeds can be sown just before the rainy season and can survive without additional irrigation if rains are spaced evenly through the winter. A glance every so often to make sure no really weedy species have dropped in is all the maintenance that is required. In spring, follow the directions above to incorporate them into the soil. Their decomposition will happen pretty quickly as the soil begins to warm. A second tilling a week or two after the initial one should be all that is needed to prepare for planting spring crops, either vegetables or that new flower border.

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